The present invention relates to a machining apparatus for machining various types of configurations (e.g., angles, surfaces, and cylinders) into a work-piece with a high precision in a short period of time. In particular, the present invention relates to a machining apparatus which comprises means for correcting distortion (such as warping) of a tool caused by a cutting resistance or grinding resistance during the machining of a curved surface of a scroll blade or a scroll wrap used in a scroll compressor. Also, the present invention relates to an internal machining apparatus which comprises means for correcting deflection (e.g., warping) of a tool and which is usable, in particular, for internal cylindrical grinding of a long hole requiring a precise cylindricality and linearity.
Conventionally, a scroll blade used in a scroll compressor has been manufactured by a machining center. However, at present scroll blades are machined by a method called simultaneous bi-axial machining in which a cutting tool is linearly moved along an involute reference curve as a work-piece is rotated. Japanese Patent Application Laid-Open Publication Nos. 6-028812 and 2-41847, for instance, disclose examples of such simultaneous bi-axial machining.
In cutting an elongated hole in a work-piece, a central axis of the hole is aligned to a work-piece rotation axis of a grinder while the work-piece is rotated about the work-piece rotation axis. At this stage, a grindstone is rotated at a high speed through a shaft of the grindstone and a spindle rotor. Next, the work-piece is ground by moving the grindstone radially outwardly of the hole. Simultaneously with this, the grindstone is moved along the rotation axis.
Meanwhile, not only in the machining with the machining center but also in the simultaneous bi-axial machining, the tool is supported at its one end away from its cutting edge. Then, the machining of the curved surface in the scroll blade for the scroll compressor causes the tool to deflect or bend when the cutting edge is subjected to a cutting resistance or grinding resistance. The deflection deviates the cutting edge of the tool from a cutting or grinding position on the involute, which in turn changes an angle of the curved surface of the scroll blade to a reference axis. In addition, not only the tool but also the work-piece or the scroll blade tend to deflect due to the cutting or grinding resistance, which causes deterioration in the precision of the machining.
To overcome those problems, the inventor of the present invention discloses, in Japanese Patent Application Laid-Open Publication No. 5-57518, a technique in which the displacement of the cutting edge is calculated in advance and then the cutting edge of the tool is configuration so that the displacement of the cutting edge relative to the work-piece cancels the displacement.
However, the curved surface of the scroll blade has a different radius of curvature depending on a place. Therefore, the deflections of the tool and the work-piece during machining of the curved surface of the scroll blade change in accordance with a position being machined. In view of the deflection of the work-piece, the work-piece tends to cause less deflection at the machining of the central portion with the smaller radius of curvature while it causes larger deflection at the machining of the peripheral portion with the larger radius of curvature. However, in view of the deflection of the tool, the deflection of the tool at the machining of the radially inwardly faced surface of the scroll blade advances in a direction that is opposite to that at the machining of the radially outwardly faced surface thereof.
Therefore, the machining of the radially inwardly faced surface of the central portion of the scroll compressor forms an enlarged length of the contact region of the tool and the work-piece, which causes an enhanced machining resistance and deflection of the tool. Also, as the machining position moves radially outwardly, the contact length decreases to reduce the deflection. Contrary to this, the machining of the radially outwardly faced surface of the scroll blade forms a reduced length of the contact region between the tool and the work-piece, which causes a reduced machining resistance and deflection of the tool. In view of above, ideally tool configuration changes according to the position of scroll blade to be machined.
In order to increase the machining precision only, the tool may be moved slowly relative to the work-piece or, as described in the Japanese Patent Laid-Open Publication No. 2-41846, the contact region between the work-piece and the tool may be extended to reduce the rotational velocity of the work-piece. However, this results in an extension of the machining time and an deterioration of the working efficiency.
Meanwhile, Japanese Patent Laid-Open Publication No. 8-318418 describes a drive system which includes a cam and a cam follower, where the cam is driven by a servo motor so that a flexible trunnion is distorted to rotate a spindle gauge. This drive system, however, due to a reduced rigidity of the trunnion, is considered unsuitable for the high-speed machining.
On the other hand, for the internal grinding of the hole, since a shaft of a grindstone is extremely long, the hole assumes a taper so that an inner diameter thereof decreases as the hole advances inwardly, which deteriorates the configuration precision in terms of cylindricality and linearity. To overcome this, another technique in which the axis of the grindstone or work-piece is intentionally tilted to offset the deflection of the tool is disclosed in Japanese Patent Laid-Open Publication Nos. 61-252064 and 62-166955, for example. However, this technique has a drawback in a responsibility and a resolution for an angle adjustment of the spindle during traversing. Another technique is disclosed in Japanese Patent Application Laid-Open Publication No. 1-240267, in which the spindle rotor axis is tilted by the use of a magnetic bearing, which is considerably costly.
The present invention has been made to solve the problems above. Means to solve the problems are as described below.
More specifically, according to a first aspect of the present invention, in a machining system for machining an internal surface of a work-piece, with respect to four axes in total which are a Z-axis in the direction of depth of an internal wall of the work-piece, an X-axis perpendicular to the Z-axis and in the direction for feeding the tool, a Y-axis perpendicular to the Z-axis and the X-axis, and a work-piece C-axis parallel to the Z-axis, the work-piece and the tool are movable relative to each other about at least two axes of the X-axis and the Z-axis, the relative movement between the work-piece and the tool can be corrected simultaneously with respect to the two axes, a rotation axis of the work spindle and a rotation axis of the spindle primary-axis portion can rotate relative to each other at a resolution even as fine as in seconds (angles) to thereby correct a machining error created as a machining condition changes, and a central axis of the relative rotation does not move relative to a machining point even when the work-piece and the tool move relative to each other under machining.
According to other aspect of the present invention, in the machining system, relative rotation between the work-piece and the rotation axis of the spindle primary-axis portion for correction of the machining error may be relative rotation about two axes, an A-axis parallel to the X-axis and a B-axis parallel to the Y-axis.
According to other aspect of the present invention, in the machining system, it is preferable that of the relative rotation about the two axes of the A-axis and the B-axis, the work-piece is driven in the relative rotation about one of the two axes, while the spindle primary-axis portion is driven in the relative rotation about the other one of the two axes.
According to a different aspect of the present invention, in a machining system for machining a scroll blade, with respect to mutually perpendicular three axes in total which are a Z-axis in the direction of depth of a vortex, an X-axis perpendicular to the Z-axis and in the direction for feeding the tool, and a Y-axis perpendicular to the Z-axis and the X-axis, the work-piece and the tool are movable relative to each other about at least the X-axis and the Z-axis, it is possible to simultaneously control movements about at least the two axes, which are relative movement in the direction of the X-axis and rotation about a C-axis (an axis parallel to the Z-axis) which is an axis of the work-piece, a rotation axis of the work spindle and a rotation axis of the spindle primary-axis portion can rotate relative to each other at a resolution even as fine as in seconds (angles) to thereby correct a machining error created as a machining condition changes, and a B-axis (an axis parallel to the Y-axis), the center of the relative rotation, does not move relative to a machining point even when the work-piece and the tool move relative to each other under machining.
According to a yet different aspect of the present invention, in a machining system for internal grinding an internal surface of a work-piece by means of traversing in the direction of a Z-axis, an axis of a cylinder of the work-piece, and by means of feeding in the direction of an X-axis perpendicular to the Z-axis and in a radius direction of the cylinder, a rotation axis of the work spindle and a rotation axis of the spindle primary-axis portion can rotate relative to each other at a resolution even as fine as in seconds (angles) to thereby correct a machining error created as a machining condition changes, and a B-axis, the center of the relative rotation, does not move relative to a machining point even when the work-piece and the tool move relative to each other under machining.
According to other aspect of the present invention, the machining system preferably comprises a rotation guide disposed between a primary-axis base where the spindle primary-axis portion is fixed and a base plate supporting the primary-axis base, and supporting the primary-axis base so as to rotate about the B-axis; an actuator providing rotational drive force to the primary-axis base supported by the rotation guide; a sensor monitoring a revolution volume about the B-axis; a data storage portion including a reference value of the revolution volume; and a feedback circuit controlling the revolution volume based on data included in the data storage portion.
According to other aspect of the present invention, in the machining system, the actuator providing the rotational drive force to the spindle primary-axis base may be a piezoelectric element, a magnetostrictive element, a feed screw mechanism driven by rotation of a motor, or a cam mechanism driving and rotating with a motor.
According to other aspect of the present invention, in the machining system, it is preferable that the data storage portion including the reference value of the revolution volume includes one among a machining error correction volume, i.e., a revolution volume about the B-axis, at each machining position, a revolution volume about the B-axis after an elapsed time since the start of each machining, an amount of distortion of the tool corresponding to a motor current of the spindle primary-axis portion and a corresponding revolution volume about the B-axis, an amount of distortion of the tool corresponding to an angle of twist of the tool or the rotation axis of the spindle primary-axis portion and a corresponding revolution volume about the B-axis, and an amount of distortion of the tool corresponding to power of the spindle primary-axis portion and a corresponding revolution volume about the B-axis, and that such data are compared with data entered in process and calculated to thereby control a revolution volume of relative rotation between the rotation axis of the work spindle and the rotation axis of the spindle primary-axis portion.
According to other aspect of the present invention, in the machining system, it is preferable that the work-piece processed based on the comparison with the data included in the data storage portion is measured at a predetermined frequency, and the data included in the data storage portion are updated sequentially based on a result of the measurement.
According to other aspect of the present invention, the machining system further comprises means for correcting relative rotation about B-axis between the rotation axis of the work spindle and the rotation axis of the spindle primary-axis portion and additionally for correcting an error in the direction of the X-axis caused by displacement of the center of the rotation about the B-axis from the spindle primary-axis portion, for the purpose of correcting warping of the tool due to the machining resistance.
According to other aspect of the present invention, in the machining system, the central axis of the relative rotation about the B-axis between the rotation axis of the work spindle and the rotation axis of the spindle primary-axis portion is arranged preferably on a machining point group or offset from the machining point group by an amount within the radius of the tool.
According to other aspect of the present invention, in the machining system, a direction in which the rotational drive force during the relative rotation about the B-axis between the rotation axis of the work spindle and the rotation axis of the spindle primary-axis portion is transmitted may be the direction of a tangential line to a circle about the B-axis.
According to other aspect of the present invention, in the machining system, it is preferable that the mechanism driving and controlling the relative rotation about the B-axis between the rotation axis of the work spindle and the rotation axis of the spindle primary-axis portion is disposed to a work-piece base seating the work spindle, and the rotation axis of the work spindle is rotated about the B-axis relative to the rotation axis of the spindle primary-axis portion.